Inductive coupling reader comprising means for extracting a power supply voltage

ABSTRACT

The present invention relates to a method for supplying a power supply voltage (Vccr) to a contactless integrated circuit reader (RD 1 ) that is in a passive operating mode, in the presence of an external alternating magnetic field (FLD 2 ), the reader comprising an antenna circuit (ACT) substantially tuned to a working frequency (F 0 ). According to the present invention, the method comprises the steps of taking off in the antenna circuit (ACT) an alternating voltage (Vcd) induced in the antenna circuit by the external magnetic field (FLD 2 ), and rectifying the induced voltage to supply an auxiliary supply voltage (Vccr).

The present invention relates to an inductive coupling reader providedfor reading contactless integrated circuits of PICC type (ProximityInductive Coupling Circuit). In the present state of technology, such areader has various names, particularly “PCD” (Proximity Coupling Device)according to the ISO/IEC standard 14443, “VCD” (Vicinity CouplingDevice) according to the ISO/IEC standard 15693, “inductive coupler” intechnical documents, etc.

The present invention relates more particularly to a reader capable ofexchanging data with another reader, in addition to exchanging data witha contactless integrated circuit.

Methods of transmitting data between inductive coupling readers arecurrently arousing considerable interest in that they offer variousprospects of application and can compete with or complete classicalwireless data transmission techniques such as Bluetooth®.

Such methods have been named “NFC” (Near Field Communication) by theindustrial community, and have a specially dedicated industrial forum(www.nfc-forum.org/home).

Inductive coupling readers embedded in mobile telephones or PDAs(personal digital assistants) are particularly concerned by NFC methods,so that data can be transferred between two mobile telephones, between amobile telephone and a PDA or vice-versa, or between a telephone or aPDA and a reader linked to a PC via a USB interface.

However, in such applications, it is essential to use readers whichconsume little electricity because an embedded reader uses the energysupplied by the battery of the mobile telephone or the PDA and thisbattery must be saved as much as possible.

European patent EP 1,327,222 in the name of the applicant describes amethod for transmitting data between two readers in which one of the tworeaders is in a passive mode and consumes little electrical energy. Thismethod, named eNFC (“enhanced NFC”), enables data to be transferredbetween a reader in passive mode and a reader in active mode orvice-versa. The reader in active mode emits a magnetic field oscillatingat a working frequency F0, such as 13.56 MHz for example, whereas thereader in passive mode does not, in principle, emit any magnetic field(except for the exception described below, in which bursts of a carriersignal are sent).

A classical architecture of a reader RDPA1 with two operating modes,active and passive, is represented in FIG. 1A. The reader RDPA1comprises the following elements:

a control circuit CCT,

an antenna circuit ACT comprising two input terminals A, B, capacitorsC1 a, C1 b, C2 a, C2 b and an antenna coil L1 having two terminals C, D,

two low-pass filters FLTa, FLTb of EMC type (EMC=electromagneticcompatibility) incorporated into the antenna circuit ACT,

an emitter circuit EMCT linked to the terminals A, B of the antennacircuit,

a demodulation circuit DEMCT and a clock extraction circuit CKCT linkedto the antenna circuit through a band-pass filter DFLT, and

a load modulation simulation circuit linked to the terminals A, B of theantenna circuit ACT, comprising a switch SW1 m in series with a loadresistor R1 m,

an oscillator CGEN supplying to the circuit EMCT a carrier signal CF0 or“carrier” CF0, of frequency F0 (working frequency of the reader,generally 13.56 MHz), and

a main supply source MPS supplying a voltage Vcc that powers the variousdevices of the reader, such as a battery or a transformer connected tothe electrical network for example.

The antenna circuit ACT is of symmetrical type and has the followingstructure:

the antenna coil L1 has a midpoint MP linked to the ground,

one terminal of the capacitor C1 a is connected to the terminal C of theantenna coil L1 and the other terminal of the capacitor is linked to theterminal A of the antenna circuit via the filter FLTa,

one terminal of the capacitor C1 b is connected to the terminal D of theantenna coil L1 and the other terminal of the capacitor is linked to theterminal B of the antenna circuit via the filter FLTb,

one terminal of the capacitor C2 a is connected to the terminal C of theantenna coil L1 and the other terminal of the capacitor is linked to theground of the reader,

one terminal of the capacitor C2 b is connected to the terminal D of theantenna coil L1 and the other terminal of the capacitor is linked to theground.

The change from the active operating mode to the passive operating mode,or vice-versa, is controlled by the circuit CCT, by means of a flagpresent in a state register (not represented) for example. A briefreminder of the characteristics of these two operating modes will begiven, each mode comprising phases of sending data and phases ofreceiving data.

Active Operating Mode

The circuit CCT activates the oscillator CGEN and the emitter circuitEMCT. The circuit EMCT applies to the antenna circuit ACT a controlsignal SX comprising the carrier CFO supplied by the oscillator CGEN.The signal SX is here split into two components SXa, SXb in oppositephase due to the symmetrical structure of the antenna circuit. Analternating antenna signal SA appears at the terminals of the antennacoil L1 and the latter emits a magnetic field FLD1 oscillating at thefrequency F0.

Data Sending in Active Mode

Sending data in active mode enables the reader RDPA1 to send data DTx toa passive contactless integrated circuit or to a reader RDPA2(represented in FIG. 1A) that is in the passive mode. To this end, thecircuit CCT applies the data DTx to the circuit EMCT and the lattermodulates the amplitude of the signal SX according to these data. Theamplitude modulation is communicated to the antenna signal SA and to themagnetic field FLD1 emitted and is detected by the reader RDPA2.

Data Receiving in Active Mode

Receiving data in active mode enables the reader RDPA1 to receive dataDTr sent by load modulation by a contactless integrated circuit or bythe reader RDPA2 in passive mode. To this end, the reader RDPA2modulates the impedance of its antenna circuit to simulate a loadmodulation that would be done by a contactless integrated circuit. Theload modulation affects the antenna circuit ACT of the reader RDPA1 anda load modulation signal SM appears in the antenna coil L1, in the formof a modulation of the envelope of the antenna signal SA. The signal SMis extracted from the antenna signal SA by the band-pass filter DFLT andis demodulated by the circuit DEMCT, which supplies the data receivedDTr to the circuit CCT.

Passive Operating Mode

The circuit CCT deactivates the emitter circuit EMCT and the oscillatorCGEN. The reader RDPA2 is put into the active mode such that the antennacoil L2 of this reader emits a magnetic field FLD2. The magnetic fieldFLD2 causes an antenna signal SA to appear in the antenna coil L1 of thereader RDPA1. This antenna signal is designated for the sake ofsimplicity by the same reference as the antenna signal of the activemode, although it appears here by inductive coupling between the antennacoils L1 and L2. The clock signal CK of the reader is extracted from theantenna signal SA by the circuit CKCT (operating mode said to be“totally passive”) or is supplied by an autonomous oscillator (notrepresented) powered by a local voltage source (operating mode said tobe “passive”).

Data Receiving in Passive Mode

Receiving data in passive mode enables the reader RDPA1 to receive dataDTr that the reader RDPA2 sends by modulating the amplitude of themagnetic field FLD2. This amplitude modulation forms, as in the case ofreceiving data in active mode, a modulation signal SM of the antennasignal SA envelope. The signal SM is extracted from the antenna signalSA by the circuit DEMCT, the latter enabling both the load modulationsignal SM received in active mode and the amplitude modulation signal SMreceived in passive mode to be extracted, the extraction involving inboth cases a demodulation of the envelope of the antenna signal.

Data Sending in Passive Mode

Sending data in passive mode enables the reader RDPA1 to send data DTxto the reader RDPA2. To this end, the circuit CCT applies a loadmodulation control signal S1 m comprising the data DTx to the switch SW1m. To simulate a load modulation that would be done by a contactlessintegrated circuit, the signal S1 m is modulated according to thestandards applicable to contactless integrated circuits, for examplewith a sub-carrier the frequency of which is a sub-multiple of theworking frequency F0 (typically 847 KHz or 424 KHz). The sub-carrier issupplied by frequency dividing circuits provided in the circuit CCT,using the clock signal CK.

Such an inductive coupling reader has the advantage of being able toexchange data with other readers in passive mode, without emitting anymagnetic field and consequently consuming little energy.

Thus, although the reader RDPA1 must be put into the active mode when itexchanges data with a contactless integrated circuit (during the readingof an electronic business card for example), it is preferably put intothe passive mode when it must transfer data to the reader RDPA2 if thelatter's electrical energy is not limited (when the reader RDPA2 is areader linked to a desktop computer and is electrically powered therebyfor example), the reader RDPA2 then being put into the active mode.

Although the electrical consumption of such a reader in passive mode islow, it nonetheless restricts the length of use of a mobile telephone orPDA battery.

To overcome this disadvantage, the present invention provides a readerthat is capable, in passive operating mode, of receiving by inductivecoupling a portion of the energy emitted by the reader in active modewith which it exchanges data.

A coil dedicated to receiving energy can be provided for that purpose.However, adding a dedicated antenna coil in a reader is a costlysolution and its incorporation into a mobile telephone or a PDA causesvarious technical problems.

Thus, the present invention provides for extracting electrical energydirectly from the antenna circuit of the reader, without using adedicated antenna coil.

More particularly, the present invention provides a method for supplyinga power supply voltage to a contactless integrated circuit reader thatis in a passive operating mode, in the presence of an externalalternating magnetic field, the reader comprising an antenna circuitcomprising at least one input terminal, at least one capacitor and anantenna coil having two end terminals, the antenna circuit beingsubstantially tuned to a working frequency and having, seen from itsinput terminal and at the working frequency, a first impedance, themethod comprising a step of taking off in the antenna circuit analternating voltage induced in the antenna circuit by the externalmagnetic field, and a step of rectifying the alternating voltage tosupply an auxiliary supply voltage.

According to one embodiment, the method comprises the steps of applyingto the input terminal of the antenna circuit a control signal having anelectric potential by default such that the antenna circuit has a higherimpedance point at which its impedance is higher than the firstimpedance, and taking off the alternating voltage at the higherimpedance point without going through the input terminal.

According to one embodiment, the alternating voltage is taken off on atleast one terminal of the antenna coil.

According to one embodiment, the alternating voltage is rectifiedwithout clipping the induced alternating voltage.

According to one embodiment, the alternating voltage is taken off on oneof the end terminals of the coil.

According to one embodiment, the alternating voltage is taken off on oneterminal of the antenna coil that is not at the end of the coil andwhich forms a dividing point of the induced alternating voltage.

According to one embodiment, the auxiliary supply voltage is suppliedduring a data receiving phase of the reader in passive operating mode.

According to one embodiment, the auxiliary supply voltage is alsosupplied during a data sending phase of the reader in passive operatingmode.

According to one embodiment, the method is applied to a readercomprising an internal power supply line linked to a main power supplysource, supplying a main supply voltage, and comprising injecting theauxiliary supply voltage into the internal supply line and blocking themain supply voltage when the auxiliary supply voltage is injected intothe internal supply line.

According to one embodiment, the default electric potential of thecontrol signal is the high impedance potential, or the 0 potential,corresponding to the ground potential of the reader.

According to one embodiment, the method comprises a step of switchingthe control signal into a second electric potential in addition to thedefault electric potential, so as to cause a modification to theimpedance of the antenna circuit, to cause a load modulation in theantenna coil of another reader and to send data in passive mode by meansof the antenna circuit.

According to one embodiment, the control signal in passive mode has oneof the following combinations of states: 1) by default, the 0 potential,and the high impedance potential to simulate a load modulation; 2) bydefault, the high impedance potential, and the 0 potential to simulate aload modulation; 3) by default, the 0 potential, and a direct voltage tosimulate a load modulation; 4) by default, the high impedance potential,and a direct voltage to simulate a load modulation; 5) by default, the 0potential, and an oscillating electric signal to simulate a loadmodulation; 6) by default, the high impedance potential and anoscillating electric signal to simulate a load modulation.

The present invention also relates to an inductive coupling readerhaving an active operating mode and a passive operating mode andcomprising: an antenna circuit substantially tuned to a workingfrequency, comprising at least one input terminal, at least onecapacitor, and an antenna coil having two end terminals, the capacitorand the coil being chosen so that the antenna circuit is substantiallytuned to a working frequency and has, at the working frequency and seenfrom its input terminal, a first impedance; an emitter circuit forapplying to the input terminal of the antenna circuit, when the readeris in the active operating mode, an excitation signal oscillating at theworking frequency, so that the antenna coil emits a magnetic field, andfor modulating the excitation signal to send data; an auxiliary supplycircuit linked to the antenna circuit and arranged for supplying anauxiliary supply voltage of the reader using an alternating voltageinduced in the antenna circuit by an external magnetic field.

According to one embodiment, the reader comprises a circuit for applyingto the input terminal of the antenna circuit, in the passive operatingmode, a control signal having an electric potential by default such thatthe antenna circuit has a higher impedance point at which its impedanceis higher than the first impedance, and the auxiliary supply circuit islinked to the higher impedance point without going through the inputterminal of the antenna circuit.

According to one embodiment, the auxiliary supply circuit is linked toat least one terminal of the antenna coil.

According to one embodiment, the auxiliary supply circuit comprises aninput stage without a clipper diode for clipping the induced alternatingvoltage.

According to one embodiment, the auxiliary supply circuit is connectedto one of the end terminals of the coil.

According to one embodiment, the auxiliary supply circuit is connectedto one terminal of the coil that is not at the end of the coil and whichforms a dividing point of the induced alternating voltage.

According to one embodiment, the auxiliary supply circuit comprises atleast one rectifying diode for rectifying the alternating voltage and acapacitor for low-pass filtering the rectified voltage.

According to one embodiment, the auxiliary supply circuit supplies theauxiliary supply voltage during a phase of receiving data in passiveoperating mode.

According to one embodiment, the auxiliary supply circuit also suppliesthe auxiliary supply voltage during a phase of sending data in passiveoperating mode.

According to one embodiment, the reader comprises an internal powersupply line linked firstly to a main power supply source and secondly tothe auxiliary supply circuit.

According to one embodiment, the internal supply line is linked to themain supply source and to the auxiliary supply circuit through a circuitthat blocks a voltage proceeding from the main supply source when theauxiliary supply voltage is present.

According to one embodiment, the default electric potential of thecontrol signal is the high impedance potential or the 0 potential,corresponding to the ground potential of the reader.

According to one embodiment, the reader comprises a circuit for takingthe control signal into a second electric potential in addition to thedefault electric potential, in order to cause a modification to theimpedance of the antenna circuit at the working frequency and to senddata in passive operating mode.

According to one embodiment, the control signal in passive mode has oneof the following combinations of states: 1) by default, the 0 potential,and the high impedance potential to simulate a load modulation; 2) bydefault, the high impedance potential, and the 0 potential to simulate aload modulation; 3) by default, the 0 potential, and a direct voltage tosimulate a load modulation; 4) by default, the high impedance potential,and a direct voltage to simulate a load modulation; 5) by default, the 0potential, and an oscillating electric signal to simulate a loadmodulation; 6) by default, the high impedance potential and anoscillating electric signal to simulate a load modulation.

According to one embodiment, the emitter circuit supplies the controlsignal applied to the input terminal of the antenna circuit in thepassive operating mode.

According to one embodiment, the control signal is taken to the secondelectric potential by the emitter circuit.

The present invention also relates to a portable electronic devicecomprising means for processing data and a rechargeable battery,particularly a mobile telephone or a personal digital assistant,comprising a reader according to the present invention.

According to one embodiment of the portable electronic device, thereader in the active operating mode is powered by the battery of theportable device, and is self-powered by the auxiliary supply circuit inthe passive operating mode.

These and other objects, features and advantages of the presentinvention will be explained in greater detail in the followingdescription of the method according to the present invention and of anexample of embodiment of an inductive coupling reader according to thepresent invention, given in relation with, but not limited to thefollowing figures:

FIG. 1A represents the architecture of a classical inductive couplingreader,

FIG. 1B represents the reader in FIG. 1A equipped with a means forreceiving electrical energy by inductive coupling,

FIGS. 2A, 2B, 2C show a method according to the present inventionenabling a reader to receive electrical energy by inductive couplingwhile receiving or sending data, the method here being applied to asymmetrical antenna circuit,

FIGS. 3A, 3B are equivalent diagrams of the antenna circuit inconfigurations shown in FIGS. 2A to 2C,

FIG. 4 shows the same method applied to a non-symmetrical antennacircuit,

FIGS. 5A, 5B, 5C represent various embodiments of an auxiliary supplycircuit according to the present invention,

FIG. 6 represents the general architecture of an inductive couplingreader according to the present invention,

FIG. 7 represents the structure of a port of an emitter circuit presentin the reader in FIG. 6,

FIGS. 8A, 8B, 8C represent signals appearing in the reader in FIG. 6when the latter sends data in passive mode, and

FIGS. 9A, 9B, 9C represent signals appearing in a reader in active modelinked to the reader in FIG. 6 by inductive coupling.

According to a first aspect of the present invention, electrical energyis directly extracted from the antenna circuit of an inductive couplingreader, without equipping the reader with an additional coil.

FIG. 1B shows the implementation of this aspect of the present inventionin the reader RDPA1 described above in relation with FIG. 1A. Thegeneral structure of the reader RDPA1 remains unchanged, and the sameelements are designated by the same references.

The antenna circuit ACT comprises, between its input terminals A, B, thecoil L1 the midpoint MP of which is linked to the ground GND, thecapacitors C1 a, C1 b, C2 a, C2 b and the filters FLTa, FLTb. The filterFLTa comprises for example a coil 10 a connected between the terminal Aand the capacitor C1 a, and a capacitor 11 a connected between thecapacitor C1 a and the ground. The filter FLTb is identical to thefilter FLTa and comprises a coil 10 b connected between the terminal Band the capacitor C1 b, and a capacitor 11 b connected between thecapacitor C1 b and the ground.

The antenna circuit ACT is classically a resonant circuit setsubstantially to the working frequency F0, “substantially” meaning towithin a few hundred KHz, for example with a difference in the order of0 to Fsc relative to the frequency F0, Fsc being the frequency of asub-carrier used for the load modulation, such as 847 KHz for example.Providing such a difference is within the know-how of those skilled inthe art and is aimed solely at optimising the receipt of the sub-carrierin active mode.

According to the present invention, the following elements are added tothe reader RDPA1:

two switches SW1 a, SW1 b between the outputs of the emitter circuitEMCT and the terminals A, B of the antenna circuit,

a diode rectifier bridge Pd comprising a smoothing capacitor Cs atoutput, and

two switches SW2 a, SW2 b linking the inputs of the rectifier bridge tothe terminals A, B of the antenna circuit.

Thus, when the reader RDPA1 is in the active operating mode, the controlcircuit CCT closes the switches SW1 a, SW1 b and opens the switches SW2a, SW2 b. The circuit EMCT is linked to the terminals A, B of theantenna circuit ACT and applies to the latter the control signal SXcomprising the carrier CF0 of frequency F0, and split into twocomponents SXa, SXb.

In the passive operating mode, the circuit CCT deactivates the circuitEMCT and the oscillator CGEN, opens the switches SW1 a, SW1 b and closesthe switches SW2 a, SW2 b. Thus, the rectifier Pd is connected to theterminals A, B of the antenna circuit. In the presence of a magneticfield FLD2 emitted by another reader RDPA2, the rectifier Pd receives analternating voltage Vab that varies, on the one hand, according to thevoltage Vcd of the antenna signal SA induced in the coil L1, i.e. thevoltage appearing between the terminal C of the coil L1 and the midpointMP (this voltage also appearing between the terminal D of the coil andthe midpoint MP) and, on the other hand, according to the impedance ofthe antenna circuit seen from the terminals A, B. The rectifier Pd thensupplies an auxiliary supply voltage Vccr, by rectifying the voltageVab.

The clock signal CK of the reader is extracted from the antenna signalSA by the circuit CKCT or is supplied by an autonomous oscillator (notrepresented) that could be powered by the voltage Vccr.

Although this mode of receiving electrical energy by inductive couplingmeets the intended aim of the present invention in principle, is doeshave a disadvantage. Indeed, the antenna circuit ACT is generallyprovided to have a high quality factor and low impedance at the workingfrequency F0, generally only a few tens of ohms, so that the magneticfield FLD1 emitted in active mode has a maximum amplitude in response tothe control signal SX supplied by the circuit EMCT. Now, such low valueof the antenna circuit impedance is contrary to the electrical energybeing properly received since such energy is partly consumed in theantenna circuit, such that the current which can be supplied by theauxiliary supply circuit is low.

In these conditions, the auxiliary voltage Vccr cannot be used todirectly power the reader RDPA1. It can only be used to partiallyrecharge the main power supply source MPS if this is a battery, or toslowly charge up a backup battery.

Those skilled in the art will understand that it is not possible toconsider solving this disadvantage by giving the antenna circuit highimpedance at the working frequency F0, because the primary function ofthe reader is to read passive contactless integrated circuits andpriority must be given to optimising its operation in active mode.

Thus, the present invention also aims to provide a method wherebyelectrical energy can be extracted from the antenna circuit with a goodyield without the need to modify the impedance of the antenna circuit atthe working frequency.

To this end, the present invention is first of all based on a findingdisclosed by European patent EP 1,327,222 (above-mentioned), whereby areader in passive mode can send data to another reader by applying acontrol signal with two states to the input terminals A, B of itsantenna circuit. Such a signal with two states makes it possible tosimulate a load modulation that would be done by a contactlessintegrated circuit. According to European patent EP 1,327,222, thestates that can be applied to the terminals A, B of the antenna circuitare for example the following:

0 (ground of the reader),

HZ (high impedance),

“1”, i.e. a direct voltage Vcc, or

a burst of the carrier CFO.

The present invention is subsequently based on the observation that someof these states, particularly the 0 and HZ electric potentials, cause anincrease in the impedance of the antenna circuit at certain points ofthe antenna circuit, particularly on the terminals C, D of the antennacoil.

Thus, as a higher impedance guarantees a better receipt of theelectrical energy by inductive coupling, the present invention providesfor:

1) applying one of these states or electric potentials to the terminalsA, B of the antenna circuit, and

2) producing the auxiliary supply voltage Vccr using an alternatingvoltage taken off at a higher impedance point of the antenna circuit,preferably using the voltage Vcd taken off on the terminals C and/or Dof the antenna coil L1, instead of producing the voltage Vccr using thevoltage Vab present on the terminals A, B of the antenna circuit.

The method according to the present invention thus comprises thefollowing operations:

when the reader RD1 is in passive mode and is awaiting data or isreceiving data, applying to the terminals A, B of the antenna circuitthe default state that is defined as being the best electric potentialfor properly receiving the energy, such as the 0 or HZ potential forexample,

when the reader is sending data in passive mode, changing from thedefault state to another state so as to simulate a load modulation.

The state enabling a load modulation to be simulated is preferably theHZ electric potential if the 0 electric potential is the default stateor the 0 electric potential if the HZ electric potential is the defaultstate.

The state “1” or electric potential Vcc can also be used to simulate aload modulation, in combination with the default state 0 or HZ, byproviding short pulses of voltage Vcc. Thus, if the load modulationsimulation is paced by a sub-carrier of 847 KHz, the duration of theload modulation simulation pulses is equal to R*1/847*10³ ms, R beingthe duty factor of the pulses, i.e. 0.59 ms if the pulses have a dutyfactor equal to 0.5, and 0.3 ms if these pulses have a duty factor equalto 0.25.

Equally, the present invention does not rule out using the state called“carrier bursts” to simulate a load modulation, in combination with the0 or HZ potential as default state, provided the reader is equipped witha high-value smoothing capacitor capable of compensating for analteration in the receipt of the energy during the periods in whichcarrier bursts are sent (this point will be discussed below).

In summary, the possible combinations of states are the following (thefirst state designated in each combination being the default state):

combination 1: {0, HZ},

combination 2: {HZ, 0},

combination 3: {0, 1},

combination 4: {Hz, 1},

combination 5: {0, “bursts of the carrier CF0”},

combination 6: {HZ, “bursts of the carrier CF0”}

FIGS. 2A, 2B, 2C show the implementation of the combinations 1, 3 and 5,respectively. These figures represent the antenna circuit ACT alreadydescribed and an auxiliary supply circuit APS according to the presentinvention. It is assumed here that the antenna circuit ACT and theauxiliary supply circuit APS are elements of a reader RD1 powered by thevoltage Vcc, the other elements of which are not represented and will bedescribed below in relation with FIG. 6.

The auxiliary supply circuit APS comprises a first input connected toone of the terminals C, D of the antenna coil L1, here the terminal C,and a second input connected to the ground GND. The terminals A, B ofthe antenna circuit receive a control signal SX1 according to thepresent invention, which here comprises two components SX1 a, SX1 b. Theswitching of the components SX1 a, SX1 b from one state to the other isoutlined by two switches CSWa, CSWb each having one output and twoinputs: the first and second inputs of each switch CSWa, CSWb receiveone of the two states or electric potentials of the control signal SX1,while the output of the switch CSWa is connected to the terminal A ofthe antenna circuit and the output of the switch CSWb is connected tothe terminal B of the antenna circuit ACT.

In the presence of an external magnetic field FLD2 emitted by theantenna coil L2 of a reader RD2, an alternating antenna signal SA1 ofvoltage Vcd appears in the coil L1 by inductive coupling, between theterminal C of the antenna coil L1 and the midpoint MP or ground GND (andbetween the terminal D and the midpoint). Thus, the input of the circuitAPS receives the voltage Vcd and supplies the auxiliary supply voltageVccr by rectifying the voltage Vcd.

In the example of an embodiment shown in FIG. 2A, the first input ofeach switch CSWa, CSWb receives the 0 potential (inputs connected to theground) and the second input of each switch CSWa, CSWb receives the HZpotential (inputs in open circuit), such that the control signal SX1changes from the default 0 electric potential to the HZ electricpotential when a load modulation simulation pulse must be sent to thereader RD2.

When the signal SX1 is on 0 (SX1 a=SX1 b=0) the terminals A and B areconnected to the ground. The equivalent diagram ACTEQ1 of the antennacircuit in this configuration is represented in FIG. 3A. This equivalentdiagram is the diagram of the non-symmetrical semi-antenna circuitcomprising only half of the antenna coil L1 (designated “L1/2”, i.e. theportion of the coil extending between the node C and the midpoint MP),the capacitors C1 a, C2 a, and the filter FLTa comprising the coil 10 aand the capacitor 11 a.

When the signal SX1 is in the state HZ (SX1 a=SX1 b=HZ) the terminals Aand B are in open circuit. The equivalent diagram ACTEQ2 of the antennacircuit is represented in FIG. 3B. As the previous one, this equivalentdiagram is the diagram of the equivalent non-symmetrical semi-antennacircuit.

As it will be understood by those skilled in the art, the antennacircuit in one or other of the configurations ACTEQ1 or ACTEQ2 has, atthe working frequency F0, a higher impedance than the impedance that thesame antenna circuit has seen from the terminals A or B. Indeed, theantenna circuit seen from the terminals A or B is a serial/parallelcircuit LC whereas the antenna circuit seen from the terminal C or D isa parallel circuit LC in the configurations ACTEQ1, ACTEQ2. Moreparticularly:

1) in the configuration ACTEQ1 the coil L1 is in parallel with thecapacitor C2 a and is also in parallel with an impedance EZ1. Thisimpedance EZ1 is formed by the capacitor C1 a in series with animpedance EZ2. The impedance EZ2 is formed by the capacitor 11 a of thefilter FLTa in parallel with the coil 10 a of the filter FLTa (becausethe end of the coil 10 a is connected to the terminal A of the antennacircuit, which is connected to the ground).2) in the configuration ACTEQ2, the coil L1 is in parallel with thecapacitor C2 a and with an impedance EZ1′. This impedance EZ1′ is formedby the capacitor C1 a in series with the capacitor 11 a of the filterFLTa (as the end of the coil 10 a connected to the terminal A is in opencircuit, the coil 10 a is not taken into account).

Of these two configurations, the one that has the highest impedancedepends on the values given to the components L1, C1 a, C1 b, C2 a, C2b, 10 a, 11 a, 10 b, 11 b. These values can be chosen at the time ofdesigning the antenna circuit using software calculation and simulationtools, to determine in advance the configuration of the highestimpedance. However, out of a set of possible values of the values of thecomponents L1, C1 a, C1 b, C2 a, C2 b, FLTa, FLTb, it emerges that theconfiguration ACTEQ1 generally has a higher impedance than theconfiguration ACTEQ2, such that, against all expectations, the state 0is the preferred default state of the control signal SX1 in passivemode.

These observations also apply to the example of an embodiment shown inFIG. 2B, in which the default state of the signal SX1 is the 0 potentialand the state enabling a load modulation to be simulated is the directvoltage Vcc. Thus, the electrical energy is optimally received when thereader receives or is waiting to receive data. When the direct voltageVcc is applied to the antenna circuit, this voltage is superimposed onthe induced alternating voltage Vcd but does not prevent the electricalenergy from being received.

In the example of an embodiment shown in FIG. 2C, the switches CSWa,CSWb receive at their first input the 0 potential (default potential)and receive at their second input the carrier CF0, the latter beingapplied to the switch CSWa without phase shift and to the switch CSWbwith a phase shift of 180° (F0−π) so that the signals SX1 a, SX1 b donot cancel each other out. As the load modulation simulation isgenerally done with the sub-carrier Fsc the frequency of which is asub-multiple of the carrier F0, each burst of the carrier CFO forming aload modulation pulse is longer than the period of the carrier (1/F0)and thus comprises several oscillations of the carrier CF0. For example,a carrier of frequency F0=13.56 MHz has a period of 0.0737 ms whereas acarrier burst F0 has a duration of 0.59 ms or 0.3 ms in accordance withthe calculation done above concerning the duration of the loadmodulation pulses.

The method of the present invention is also applicable to anon-symmetrical antenna circuit without midpoint such as the antennacircuit ACT′ represented in FIG. 4. The antenna circuit ACT′ isequivalent to a symmetrical semi-antenna circuit ACT and only comprisesthe input terminal A, the filter FLTa, the capacitors C1 a, C2 a and thesemi-antenna coil L1/2 the terminal D of which is connected to theground GND. The capacitor C1 a has a terminal connected to the terminalC of the antenna coil L1/2 and a terminal connected to the terminal A ofthe antenna circuit via the filter FLTa. The capacitor C2 a has aterminal connected to the terminal C of the antenna coil and a terminalconnected to the ground GND. The signal SX1, here non-symmetrical, isapplied to the terminal A by the switch CSWa that receives at its inputsone of the combinations of states {0, HZ} {HZ, 0}, {0, 1}, {HZ, 1}, {0,“bursts of the carrier CF0”} or {HZ, “bursts of the carrier CF0”}. Theantenna circuit ACT′ is equivalent to the symmetrical antenna circuitACT and its equivalent diagram when the control signal is in the state 0or HZ is also shown by FIGS. 3A, 3B. The alternating voltage Vcd appearshere between the terminals C and D of the antenna coil L1/2.

FIGS. 5A, 5B and 5C represent examples of embodiments APS1, APS2 andAPS3 of the auxiliary supply circuit APS.

The circuit APS1 represented in FIG. 5A comprises a PN junction diode D1the anode of which (input terminal of the current in the forwarddirection of the diode) is linked to the terminal C of the antenna coiland receives the voltage Vcd. The cathode of the diode D1 supplies theauxiliary voltage Vccr (rectified voltage) and is linked to the groundthrough a smoothing capacitor Cs and a Zener diode Z1 reverse mounted inparallel with the capacitor Cs. The diode Z1 stabilizes the voltage Vccrin the vicinity of its reverse breakdown voltage, such as 5V forexample.

In one embodiment not represented in the Figures, the circuit APS islinked to the antenna coil L1 through an isolating switch, such as arelay of NO type (normally off) for example that is open when the readeris in the active mode so as to disconnect the circuit APS from theantenna coil L1.

In the circuit APS2 represented in FIG. 5B, instead of supplying thevoltage Vccr, the cathode of the diode D1 is connected to the input INRof a voltage regulator stage comprising the diode Z1, a resistor Rb anda bipolar transistor Tb. The input INR is linked to the anode of theresistor Rb and to the collector of the transistor Tb. The cathode ofthe resistor Rb is linked to the base of the transistor Tb and is alsolinked to the ground through the reverse-mounted diode Z1. The collectorof the transistor Tb forms the output OUTR of the regulator stage andsupplies the voltage Vccr.

In applications in which the voltage Vcd has significant amplitudevariations according to the communication distance, it will prove to beadvantageous to use a circuit APS having an input stage that does notclip the voltage Vcd. A regulator without clipping diode available instores under the reference 7805 will be used for example, such regulatorsupplying the voltage Vccr irrespective of the peak value of the voltageVcd.

The circuit APS3 represented in FIG. 5C is identical to the circuit APS1in FIG. 5A, but the anode of the diode D1 is connected to anintermediary terminal E of the antenna coil L1, forming a dividing nodeof the voltage Vcd that is arranged between the terminal C and themidpoint MP of the coil L1. To this end, the antenna coil L1 comprisesfor example three coils L11, L12 and L13 in series, the node E being thecrossing point of the coils L11 and L12, the midpoint MP of the coilbeing the crossing point of the coils L12 and L13. The coils L11, L12can have different impedances according to the voltage Vcd dividing raterequired. The sum of the impedances of the coils L11 to L13 is equal tothe impedance desired for the antenna coil L1. Assuming the impedance ofthe coil L11 is equal to that of the coil L12 and equal to half theimpedance of the coil L13, the node E supplies a voltage Vcd′ equal toVcd/2.

FIG. 6 is an overview of the reader RD1 according to the presentinvention and also represents the reader RD2 with which the reader RD1is capable of exchanging data. The reader RD1 comprises:

a control circuit CCT1, for example a microprocessor or microcontrollerequipped with peripheral circuits and particularly a program memory anda data memory (not represented),

the antenna circuit ACT already described,

a classical demodulation circuit DEMCT and a classical clock extractioncircuit CKCT linked to the antenna circuit through a band-pass filterDFLT, the references already used to designate these elements beingmaintained,

an emitter circuit EMCT1 according to the present invention, comprisingports P1 and P2 respectively linked to the terminals A and B of theantenna circuit ACT,

an oscillator CGEN supplying the carrier CF0 of frequency F0 to thecircuit EMCT1,

a main power supply source MPS, such as a battery for example, supplyingan external supply voltage Vcce, and

the auxiliary supply circuit APS already described, connected to theterminal C of the antenna coil L1 and supplying the auxiliary supplyvoltage Vccr.

According to one aspect of the present invention, the external supplyvoltage Vcce and the auxiliary supply voltage Vccr are sent in a commonpower supply line IPSL that supplies the voltage Vcc powering all of theelements of the reader RD1. More particularly, the voltage Vcce isapplied to the line IPSL through a forward-biased diode PSD1 and thevoltage Vccr is applied to the line IPSL through a forward-biased diodePSD2. In passive mode, when the magnetic field FLD1 generated by thereader RD2 causes the voltage Vccr to appear and when the latter becomeshigher than the voltage Vcce, the diode PSD1 is blocked and the readeris powered by the voltage Vccr (Vcc=Vccr). In active mode, the reader ispowered by the voltage Vcce (Vcc=Vcce).

According to another aspect of the present invention, the emittercircuit EMCT1 supplies the control signal SX1 both in the active modeand in the passive mode, through the ports P1, P2. The latter are thusconnected directly to the terminals A, B of the antenna circuit, withoutany switch of the type represented in FIGS. 2A to 2C being needed.

Thus, when the reader RD1 is in the active mode, the signal SX1 (herecomprising two symmetrical components SX1 a, SX1 b) is an excitationsignal comprising the carrier CFO and which is amplitude modulated whendata DTx must be sent.

When the reader RD1 is in the passive mode, the signal SX1 has a defaultstate and a state whereby a load modulation can be simulated. Asdescribed above, the default state is preferably the 0 potential or theHZ potential, and the state for the load modulation simulation is to bechosen from the states 0, 1 (Vcc), HZ and “carrier bursts”.

FIG. 7 represents an example of an embodiment of the ports P1, P2 of theemitter circuit EMCT1. The port P1, P2 represented receives the carrierCF0 with or without phase shift (depending on the port considered) andis driven by a combination of control signals SETHZ (“Set High-Z”), CEN(“Carrier Enable”), SET1 (“Set to 1”). The port P1, P2 representedcomprises an AND-type gate AG with two inputs, an OR-type gate OG withtwo inputs and a tri-state inverting buffer TIB. The gate AG receivesthe carrier CF0 and the signal CEN. The gate OG receives the outputsignal of the gate AG and the signal SET1. The output signal of the gateOG is applied to the buffer TIB that receives the signal SETHZ at acontrol input, the output of the buffer TIB supplying the control signalSX1 (or one of the components SX1 a, SX1 b).

Table 1 below describes the combinations of control signals that thecircuit CCT1 can apply to the circuit EMCT1 when the reader RD1 is inthe active mode, so that the circuit EMCT1 supplies the carrier (SX1=F0)or the state 0 (ground), this state corresponding to a 100% modulationof the amplitude of the antenna signal SA1 (sending data in activemode).

It will be noted here that an amplitude modulation below 100%, such as a10% amplitude modulation for example as provided for by ISO standard14443/B, can also be obtained by applying the finding described byEuropean patent EP 1163718. In this case, several ports of the typerepresented in FIG. 7, such as six ports for example, are provided.Three ports are connected in parallel to the terminal A of the antennacircuit and three other ports are connected in parallel to the terminalB of the antenna circuit. The ports are individually driven by differentcombinations of control signals. To modulate the amplitude of theantenna signal SA1 with a modulation amplitude below 100%, certain portsare taken into the state HZ while others supply the carrier CF0.

Table 2 below describes the combinations of control signals that thecircuit CCT1 can apply to the circuit EMCT1 when the reader RD1 is inthe passive mode, to apply one of the states 0, 1 (Vcc), HZ or “burstsof the carrier C0”.

Except when the “carrier bursts” state is used to simulate a loadmodulation, the oscillator CGEN is in principle switched off so as tolimit the electrical consumption of the reader.

TABLE 1 Control signals of the circuit EMCT1 (active mode) No. F0 CENSET1 SETHZ SX1 1 F0 0 0 0 0 2 F0 0 0 1 HZ 3 F0 0 1 0 1 4 F0 0 1 1 HZ(redundant with 2) 5 F0 1 0 0 F0 6 F0 1 0 1 HZ (redundant with 2 and 4)7 F0 1 1 0 (not used) 8 F0 1 1 1 (not used)

TABLE 2 Control signals of the circuit EMCT1 (passive mode) No. F0 CENSET1 SETHZ SX1 1 — 0 0 0 0 2 — 0 0 1 HZ 3 — 0 1 0 1 4 — 0 1 1 HZ(redundant with 2) 5 — 1 0 0 (not used) 6 — 1 0 1 (not used) 7 — 1 1 0(not used) 8 — 1 1 1 (not used)

According to yet another aspect of the present invention, the input ofthe gate OG receiving the signal SET1 (FIG. 7) is linked to the lineIPSL via a pull-up resistor Rpu. Thus, if the reader RD1 is switched offby opening a switch PSSW arranged between the source MPS and theinternal power supply line IPSL (FIG. 6), the reader can nonethelessactivate itself automatically in the presence of the magnetic field FLD2emitted by the other reader RD2. In this case, the voltage Vcc=Vccrappears on the line IPSL and the output of the gate OG is forced to 1.As a consequence, the signal SX1 at the output of the buffer changes bydefault to 0, such that the antenna circuit ACT is in the bestconfiguration for receiving the electrical energy by inductive coupling,until the control circuit CCT1, after executing initialisation phases,takes control of the ports P1, P2. It shall be noted that a similarmeasure can be provided for forcing the signal SETHZ to 1, if the bestdefault state for receiving the energy is the state HZ.

As an illustration of the foregoing description, FIGS. 8A, 8B, 8C, 9A,9B, 9C represent signals appearing in the reader RD1 and in the readerRD2 when the reader RD1 in passive mode sends data to the reader RD2 inactive mode. These Figures are divided into three parts EX1, EX2, EX3each showing an example of data transmission in passive mode accordingto one of the six combinations of states described above.

FIG. 8A represents the control signal SX1 applied to the antenna circuitACT of the reader RD1. FIG. 8B represents the antenna signal SA1 of thereader RD1. FIG. 8C represents the magnetic field FLD1 emitted by thereader RD1. FIG. 9A represents the magnetic field FLD2 emitted by thereader RD2. FIG. 9B represents a control signal SX2 that the reader RD2applies to its antenna circuit (although not detailed in FIG. 6, thestructure of the reader RD2 is here considered to be identical to thatof the reader RD1). FIG. 9C represents the load modulation signal SM2that the reader RD2 extracts from its antenna circuit.

In the example “EX1”, the default state of the signal SX1 is 0 and thestate of the signal SX1 for the load modulation simulation is HZ. In theexample “EX2”, the default state of the signal SX1 is 0, the state ofthe signal SX1 for the load modulation simulation is 1 (Vcc). In theexample EX3, the default state of the signal SX1 is 0, the state of thesignal SX1 for the load modulation simulation is the “bursts of thecarrier CF0” state.

It emerges from these figures that the excitation signal SX2 applied tothe antenna circuit of the reader RD2 oscillates at the workingfrequency F0 but has a constant amplitude (FIG. 9B) since the reader RD2does not send any data. However, the signal SX1 that the reader RD1applies to its antenna circuit (FIG. 8A) has state changes (simulationof a load modulation) which cause a modulation of the envelope of themagnetic field FLD2 emitted by the reader RD2 (FIG. 9A). This envelopemodulation is detected by the reader RD2 because it forms the modulationsignal SM2 (FIG. 9C) that the reader RD2 extracts from its antennacircuit to deduce therefrom the data that the reader RD1 sends to it.Moreover, the antenna signal SA1 of the reader RD1 (FIG. 8B) copies themagnetic field FLD2 by inductive coupling, which enables the reader RD1to receive the auxiliary supply voltage Vccr. In the same way as themagnetic field FLD2, the antenna signal SA1 is modulated by the statechanges of the signal SX1. However, the amplitude of the signal SA1(which forms the voltage Vcd used to produce the voltage Vccr) is onlyslightly affected by the changes in state of the signal SX1 such thatthe supply of the voltage Vccr is not interrupted during the periods ofload modulation simulation. Example 3 (part EX3 of the Figures) in whichthe reader sends bursts of the carrier CF0, is the only case in whichthe magnetic field FLD1 emitted by the reader RD1 is not zero (FIG. 8C,EX3). The carrier bursts have been represented as being added to theantenna signal SA1 but these bursts can also cancel the antenna signalSA1 when the magnetic fields FLD1 and FLD2 are in opposite phase. Inthis case, and as indicated above, the smoothing capacitor Cs of theauxiliary supply circuit (FIGS. 5A, 5B, 5C) must have sufficientcapacity to supply the voltage Vccr while the bursts of the carrier arebeing sent.

It will be understood by those skilled in the art that variousalternative embodiments of the inductive coupling reader according tothe present invention are possible. In particular, although the examplesof embodiments of the circuit APS described are of non-symmetrical typeand take off electrical energy between one of the two points C, D andthe ground, the circuit APS can also be of symmetrical structure withmidpoint referenced to the ground and be linked to the two terminals C,D of the antenna coil L1.

Those skilled in the art will also note that the presence of thelow-pass circuits FLTa, FLTb in the antenna circuit can have aninfluence on the choice of the point used for taking off the energy inthe antenna circuit. Thus, in FIG. 6, the references G and H designatetwo other points or nodes of the antenna circuit. The point G issituated between the filter FLTa and the capacitor C1 a and wouldcorrespond to an input terminal of the antenna circuit if the latter didnot have the filter FLTa. The point H is located between the filter FLTband the capacitor C1 b and would correspond to the other input terminalof the antenna circuit if the latter did not have the filter FLTb.Additional studies that those skilled in the art could take further showthat each of the points G, H can also be used as points for taking offthe energy, particularly when the inputs A, B of the antenna circuit aretaken to high impedance (default state) since the presence of thelow-pass filters increases the impedance of the antenna circuit seenfrom these points G, H.

Generally speaking, the higher impedance point according to the presentinvention is not necessarily the point at which the antenna circuit hasthe highest impedance. The higher impedance point is a point distinctfrom the input terminals A, B of the antenna circuit providing a higherimpedance than the impedance offered by the input terminals A, B whenthe default state (0 or HZ) is applied thereto. As a numerical example,if the impedance of an antenna circuit seen from the input terminals A,B is in the order of 10Ω, the impedance of the same antenna circuit seenfrom the terminals C, D of the coil will be in the order of 1 KΩ and theimpedance of the same antenna circuit seen from the aforementionedintermediary points G, H will be in the order of 100Ω. Thus, althoughthe terminals C, D (or the terminal E, as voltage dividing point) formthe best points for taking off the electrical energy, the energy couldalso be taken off at the points G, H which offer an impedance greaterthan the 10Ω present on the terminals A, B.

1. A method for supplying a power supply voltage to a contactlessintegrated circuit reader that is in a passive operating mode, in thepresence of an external alternating magnetic field, the readercomprising an antenna circuit having at least one input terminal, atleast one capacitor and an antenna coil having two end terminals, theantenna circuit being substantially tuned to a working frequency andhaving, as measured with respect to the at least one input terminal andat the working frequency, a first impedance, the method comprising:taking off in the antenna circuit an alternating voltage induced in theantenna circuit by the external magnetic field; and rectifying thealternating voltage to supply an auxiliary supply voltage of the reader.2. The method according to claim 1, further comprising: applying to theinput terminal of the antenna circuit a control signal having anelectric potential by default such that the antenna circuit has a higherimpedance point at which its impedance is higher than the firstimpedance; and taking off the alternating voltage at the higherimpedance point without going through the input terminal.
 3. The methodaccording to claim 2, wherein the alternating voltage is taken off on atleast one terminal of the antenna coil.
 4. The method according to claim2, wherein the alternating voltage is rectified without clipping theinduced alternating voltage.
 5. The method according to claim 2, whereinthe alternating voltage is taken off on one of the end terminals of thecoil.
 6. The method according to claim 2, wherein the alternatingvoltage is taken off on one terminal of the antenna coil that is not atthe end of the coil and which forms a dividing point of the inducedalternating voltage.
 7. The method according to claim 2, wherein theauxiliary supply voltage is supplied during a data receiving phase ofthe reader in passive operating mode.
 8. The method according to claim7, wherein the auxiliary supply voltage is also supplied during a datasending phase of the reader in passive operating mode.
 9. The methodaccording to claim 2, wherein the reader further comprises an internalpower supply line coupled to a main power supply source supplying a mainsupply voltage, and the method further comprises: injecting theauxiliary supply voltage into the internal supply line and blocking themain supply voltage when the auxiliary supply voltage is injected intothe internal supply line.
 10. The method according to claim 2, whereinthe default electric potential of the control signal is one of: a highimpedance potential; and a 0 potential, corresponding to the groundpotential of the reader.
 11. The method according to claim 2, furthercomprising: switching the control signal into a second electricpotential in addition to the default electric potential, so as to causea modification to the impedance of the antenna circuit, to cause a loadmodulation in the antenna coil of another reader and to send data in thepassive mode using the antenna circuit.
 12. The method according toclaim 11, wherein the control signal in passive mode has one of thefollowing combinations of states: 1) by default, a 0 potential, and ahigh impedance potential to simulate a load modulation; 2) by default,the high impedance potential, and the 0 potential to simulate a loadmodulation; 3) by default, the 0 potential, and a direct voltage tosimulate a load modulation; 4) by default, the high impedance potential,and a direct voltage to simulate a load modulation; 5) by default, the 0potential, and an oscillating electric signal to simulate a loadmodulation; 6) by default, the high impedance potential and anoscillating electric signal to simulate a load modulation.
 13. Aninductive coupling reader having an active operating mode and a passiveoperating mode, the inductive coupling reader comprising: an antennacircuit substantially tuned to a working frequency, the antenna circuithaving at least one input terminal, at least one capacitor, and anantenna coil having two end terminals, the capacitor and the coil beingchosen so that the antenna circuit is substantially tuned to the workingfrequency and has, at the working frequency and as measured with respectto the at least one input terminal, a first impedance; an emittercircuit that applies to the input terminal of the antenna circuit, whenthe reader is in the active operating mode, an excitation signaloscillating at the working frequency, so that the antenna coil emits amagnetic field, and that modulates the excitation signal to send data;and an auxiliary supply circuit coupled to the antenna circuit andconfigured to supply an auxiliary supply voltage of the reader using analternating voltage induced in the antenna circuit by an externalmagnetic field.
 14. The reader according to claim 13, comprising acircuit for applying to the input terminal of the antenna circuit, inthe passive operating mode, a control signal having an electricpotential by default such that the antenna circuit has a higherimpedance point at which its impedance is higher than the firstimpedance, and wherein the auxiliary supply circuit is coupled to thehigher impedance point without going through the input terminal of theantenna circuit.
 15. The reader according to claim 14, wherein theauxiliary supply circuit is coupled to at least one terminal of theantenna coil.
 16. The reader according to claim 14, wherein theauxiliary supply circuit comprises an input stage without a clipperdiode for clipping the induced alternating voltage.
 17. The readeraccording to claim 14, wherein the auxiliary supply circuit is connectedto one of the end terminals of the coil.
 18. The reader according toclaim 14, wherein the auxiliary supply circuit is connected to oneterminal of the coil that is not at the end of the coil and which formsa dividing point of the induced alternating voltage.
 19. The readeraccording to claim 14, wherein the auxiliary supply circuit comprises atleast one rectifying diode that rectifies the alternating voltage and acapacitor that low-pass filters the rectified voltage.
 20. The readeraccording to claim 14, wherein the auxiliary supply circuit supplies theauxiliary supply voltage during a phase of receiving data in passiveoperating mode.
 21. The reader according to claim 20, wherein theauxiliary supply circuit also supplies the auxiliary supply voltageduring a phase of sending data in passive operating mode.
 22. The readeraccording to claim 14, comprising an internal power supply line coupledfirstly to a main power supply source and secondly to the auxiliarysupply circuit.
 23. The reader according to claim 22, wherein theinternal supply line is coupled to the main supply source and to theauxiliary supply circuit through a circuit that blocks a voltageproceeding from the main supply source when the auxiliary supply voltageis present.
 24. The reader according to claim 14, wherein the defaultelectric potential of the control signal is one of: a high impedancepotential; and a 0 potential, corresponding to the ground potential ofthe reader.
 25. The reader according to claim 14, comprising a circuitfor taking the control signal into a second electric potential inaddition to the default electric potential, in order to cause amodification to the impedance of the antenna circuit at the workingfrequency and to send data in passive operating mode.
 26. The readeraccording to claim 25, wherein the control signal in passive mode hasone of the following combinations of states: 1) by default, a 0potential, and a high impedance potential to simulate a load modulation;2) by default, the high impedance potential, and the 0 potential tosimulate a load modulation; 3) by default, the 0 potential, and a directvoltage to simulate a load modulation; 4) by default, the high impedancepotential, and a direct voltage to simulate a load modulation; 5) bydefault, the 0 potential, and an oscillating electric signal to simulatea load modulation; and 6) by default, the high impedance potential andan oscillating electric signal to simulate a load modulation.
 27. Thereader according to claim 14, wherein the emitter circuit supplies thecontrol signal applied to the input terminal of the antenna circuit inthe passive operating mode.
 28. The reader according to claim 14,wherein the control signal is taken to the second electric potential bythe emitter circuit.
 29. A portable electronic device comprising: aprocessor; a rechargeable battery coupled to the processor; and aninductive coupling reader having an active operating mode and a passiveoperating mode, the inductive coupling reader being coupled to theprocessor, the inductive coupling reader including: an antenna circuitsubstantially tuned to a working frequency, the antenna circuit havingat least one input terminal, at least one capacitor, and an antenna coilhaving two end terminals, the capacitor and the coil being chosen sothat the antenna circuit is substantially tuned to the working frequencyand has, at the working frequency and as measured with respect to the atleast one input terminal, a first impedance; an emitter circuit thatapplies to the input terminal of the antenna circuit, when the reader isin the active operating mode, an excitation signal oscillating at theworking frequency, so that the antenna coil emits a magnetic field, andthat modulates the excitation signal to send data; and an auxiliarysupply circuit coupled to the antenna circuit and configured to supplyan auxiliary supply voltage of the reader using an alternating voltageinduced in the antenna circuit by an external magnetic field.
 30. Theportable electronic device according to claim 29, wherein the reader inthe active operating mode is powered by the battery of the portabledevice, and is self-powered by the auxiliary supply circuit in thepassive operating mode.